Add blake2s hash type

Cargo.toml

@@ -6,6 +6,8 @@ authors = ["Paul Hauner <paul@paulhauner.com>"]
 [dependencies]
 ethereum-types = ""
 rand = ""
+blake2 = "^0.7.1"
+crypto-mac = "^0.6.2"
 bls = { git = "https://github.com/sigp/bls" }
 rlp = { path = "parity/util/rlp" }
 

src/state/block.rs

@@ -1,4 +1,4 @@
-use super::utils::types::{ Sha256Digest, Bitfield };
+use super::utils::types::{ Sha256Digest, Bitfield, Blake2sDigest };
 use super::utils::bls::{ Signature, AggregateSignature, Keypair, PublicKey };
 use super::aggregate_vote::AggregateVote;
 use super::rlp::{ RlpStream, Encodable } ;
@@ -11,15 +11,14 @@ pub struct Block {
     pub attestation_aggregate_sig: AggregateSignature,
     pub shard_aggregate_votes: Vec<AggregateVote>,
     pub main_chain_ref: Sha256Digest,
-    pub state_hash: Sha256Digest,
+    pub state_hash: Blake2sDigest,
     pub sig: Option<Signature>
 } 
-
 impl Block {
     pub fn new(parent_hash: Sha256Digest,
                randao_reveal: Sha256Digest,
                main_chain_ref: Sha256Digest,
-               state_hash: Sha256Digest) -> Block {
+               state_hash: Blake2sDigest) -> Block {
         Block {
             parent_hash: parent_hash,
             skip_count: 0,

src/utils/mod.rs

@@ -1,4 +1,6 @@
 extern crate ethereum_types;
+extern crate blake2;
+extern crate crypto_mac;
 
 pub mod types;
 pub mod bls;

src/utils/types.rs

@@ -1,6 +1,12 @@
 use super::ethereum_types::{ H256, H160 };
 
+pub use super::blake2::Blake2s;
+
+// TODO: presently the compiler accepts these two types
+// as interchangable. This is somewhat loose typing, 
+// which is bad. Make the compiler think they're incompatible.
 pub type Sha256Digest = H256;
+pub type Blake2sDigest = H256;
 
 pub type Address = H160;